1. Field of the Invention
The present invention relates to a wire direction changer assembly of the type described in the preamble of claim 1, i.e. to a wire direction changer assembly for installation in the wire path system of a wire electrode spark erosion machine, the assembly comprising: a wire entrance port; a wire discharge port; a substantially tube-like or tunnel-like wire guide channel connecting both ports along a curved path; and a device for providing fluid flow through the wire guide channel.
Wire direction changer assemblies of this type are known and have proven to be very useful. This holds true especially when the wire electrode breaks during unsupervised erosion operation and has to be automatically rethreaded through the workpiece.
2. Description of the Related Art
The probably first application for a patent in the field of wire return supported by fluid flow was filed in 1982, resulting in the grant of Japanese Patent 1 416 582 (MAKINO). A general description of the wire direction changer assembly can be found therein. In MAKINO, the wire direction changer assembly is basically constructed as a guide block having the shape of a housing with a wire guide channel curved at a right angle extending therethrough and supporting a guide roller for rotation therein. The wire guide channel initially extends from its wire entrance port vertically downward, subsequently transitions into a channel section curved at a right angle, which in turn runs into a straight horizontal channel section. The latter discharges into a wire discharge port, from where the wire is transported into a guide tube and subsequently conveyed to a pair of pulleys. In the guide block, there is a return pulley supported for rotation in such a way that in the section of the 90.degree. turn its periphery forms the (moving, curved) interior wall of the wire guide channel. In this region, there are two injection channels formed for injecting a pressurized liquid into the horizontal section of the wire guide channel. The injected pressurized liquid urges the wire electrode onto the periphery of the return pulley which is formed as a V-groove, and pushes or presses, as the case may be, and finally guides the wire electrode to the wire discharge port. The stream of pressurized liquid, working in a similar manner as a water jet pump, takes up any fluid remaining in the vertical section of the wire guide channel, which may consist of air or the process fluid used during spark erosion, also called dielectric.
The aforedescribed typical wire direction changer assembly was later modified as, for example, described in the Japanese Patent 1 974 770 (MITSUBISHI DENKI) and the corresponding Patents DE 39 91 621 T1 or U.S. Pat. No. 5,073,691. In contrast to the prior state of the art, the latter wire direction changer assembly moves the location for injecting the pressurized liquid to the region of the wire entrance port, thereby pushing or pressing the electrode wire through the wire guide channel from the beginning to the end.
An improvement of the wire direction changer assembly described last can be found in the Japanese patent 1 951 281 (MITSUBISHI DENKI). Here, injection of the pressurized liquid still remains in the region of the wire entrance port, although in this case aided by a suction nozzle which sucks the wire electrode from the outside into the wire entrance port, but the wire electrode is once more pushed or pressed through the entire wire guide channel.
A corresponding embodiment can also be found in the Japanese patent 2 5525 234 (MITSUBISHI DENKI) and the corresponding patents DE 39 42 957 A1 or U.S. Pat. No. 5,126, 524. A wire direction changer assembly of this design has also bee older German patent application of the Applicant (AGIE) with the reference number 196 07 705.2.
Under unfavorable conditions, in particular with today's very thin wire electrodes frequently in use having, for example, a diameter of 0.1 to 0.3 mm or less, malfunctions may occur in the region of the curved wire guide channel in spite of the significant advantages provided by the aforedescribed fluid-supported wire return. Frequently, the electrode wire which is pushed or pressed by the pressurized liquid, bumps in this region against the outside wall, thereby roughening the wall over time and impairing the flow conditions.
A wire return not supported by fluid is known from JP-A-6 126 537 (FANUC). There the wire direction changer assembly neither includes a substantially tube-like or tunnel-like wire guide channel nor a device for generating a fluid flow; in particular, no device for generating a fluid flow through a non-existing wire guide channel.